A conventional electromagnetic actuator for opening and closing a valve of an internal combustion engine generally includes "open" and "close" electromagnets which, when energized, produce an electromagnetic force on an armature. The armature is biased by a pair of identical springs arranged in parallel. The armature is coupled with a gas exchange valve of the engine. The armature rests approximately half way between the open and close electromagnets when the springs are in equilibrium. When the armature is held by a magnetic force in either the closed or opened position (at rest against the open or close electromagnet), potential energy is stored by the springs. If the magnetic force is shut off with the armature in the opened position, the spring's potential energy will be converted to kinetic energy of the moving mass and cause the armature to move towards the close electromagnet. If friction is sufficiently low, the armature can then be caught in the closed position by applying current to the close electromagnet.
Generally, each electromagnet of a conventional electromagnetic actuator comprises a plurality of stacked laminations joined to define the core of the actuator. This core design offers the advantage of high efficiency by minimizing eddy current loses in the magnetic material. However, a disadvantage of this design is that machining of the laminations must be performed in a plane perpendicular to the orientation of the laminations which tends to cause the laminations to spread apart. This may result in poor dimensional control and burr formation. Furthermore, an aperture is generally provided through the core to receive a press-fit bushing to support a reciprocating shaft of the actuator. The stacked lamination core design cannot support the press-fit bushing due to the spreading of the individual laminations.
Accordingly, there is a need to provide an electromagnetic actuator having a core assembly which minimizes eddy currents yet is capable of receiving a bushing to support a reciprocating shaft.